Electronic control for alternating



W. H. ELECTRONIC CONTROL FOR AL Sept. 11, 1951 ELLIOT Re. 23,410

TERNATING CURRENT TRANSLATING DEVICES Original Filed April 9, 1945 2 SheetLs-Sheef 1 ubqkok Sept. 11, 1951 w. H. ELLIOT ELECTRONIC CONTROL FOR ALTERNA'IING CURRENT TRANSLATING DEVICES Original Filed April 9. 1945 2 Sheets-Sheet 2 rwgmx l m 5 3&6

VOLTAGE \J MINIMUM VALUE Lu ro/z :TABLE 1 a cowucr/o/v a 00?- Q 0 0 a n3 '5- 1 W10 g5 1 MIN. 4:: E M 0% UMSTABLE USEFUL RANGE [00% 0% UNJTABLE USEFUL mus: 1 ZUBECONDUCT/ON @ERCENTAGE 0/ FULL CONDUCT/0N) TUBE CONDUCT/0N (PERCENTAGE OF FULL CONDUCT/0N) L L L \J k d STOP M W o 0-J l Reissued Sept. 11, 1951 ELECTRONIC CONTROL FOR ALTERNATING CURRENT TRANSLATING DEVICES William H. Elliot, Shorewood, Wis., assignor t Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Original No. 2,448,256, dated August 31, 1948, Se-

rial No. 587,245, April 9, 1945. Application for reissue June 16, 1949, Serial No. 99,531

27 Claims.

Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

The invention relates to the control of alternating current [motors] translating devices and, while not limited thereto, it is especially suitable for the automatic speed control of polyphase induction motors, and, more particularly, motors of the slip-ring type.

The speed of slip-ring type motors, which are required to exert a relatively constant torque, may be varied between zero and synchronous speed by varying the resistance in the secondary circuit. As the commutation of the secondary resistance involves mechanical elements having inertia and electrical circuits having inductance, such speed control is not suitable when the torque required of the motor varies rapidly, as for any given adjustment of the secondary resistance the speed varies substantially inversely as the torque. Furthermore, if the torque required under certain operating conditions is only a small fraction of the normal torque of the motor, while at the same time the speed required is only a small fraction of the normal speed. and at other times the speed and the corresponding torque are high, the material required for the secondary resistance and the amount of apparatus for commutating such resistance become abnormally high and complicated. It has therefore become customary under these conditions to employ special means such as multi-speed motors with a plurality of primary and/or secondary windings or two separate motors, one for the high speeds and torques and the other for the low speeds and low or high torques. Where two motors are employed, the motor for the low speed may be geared down so as to afiord high torque with a small motor.

The present invention obviates the aforementioned disadvantages. It employs a system which, operating with a single standard induction motor, affords accurate maintenance of any desired speed between zero and maximum speed for any load between zero and the maximum torque which the motor is capable of exerting and irrespective of the rapidity of variations of the load imposed upon the motor.

A preferred form of the system embodying the present invention employs a three-phase slipring type induction motor which is provided with a commutable secondary resistor and with a variable impedance in one of the three lines to the primary terminals of the motor. By increasing this impedance, the primary magnetic field of the motor becomes unbalanced and this results in a reduction in the torque exerted by the motor,

such reduction varying with the amount of unbalance.

Figure 1 of the accompanying drawings illustrates the relation of the phase currents supplied to an induction motor and the torque exerted by the latter. The diagram illustrates stalled characteristics for an induction motor having a given secondary resistance and it will be noted that when the currents of the three phases are balanced the torque is a maximum, whereas the torque decreases with the unbalancing of the phase currents and becomes zero when the current in one of the phases is zero.

As shown by the diagram, the current I in phase 3 is gradually reduced from its maximum value to zero. When the current in phase 3 is a maximum, the currents I and I in phases I and 2, respectively, are also a maximum and equal to the current in phase 3. As the current in phase 3 is reduced, the currents in phases l and 2 remain substantially constant, although they slightly differ from each other due to the dissymmetry created by the unbalancing. When the current in phase'3 is zero, the currents in phases 1 and 2 are again equal to each other and substantially equal to the current obtaining when the phases are balanced. Similar conditions to those described obtain with any adjustment of the secondary resistance except that the primary current values are proportionally increased or decreased, and the same relation holds true for various speeds especially for very low speeds of the motor. At higher speeds, the conditions are somewhat modified due to the counter-magnetomotive forces of the rotating secondary winding. However, the present control of the impedance in one line to a polyphase motor is primarily of interest in connection with a high secondary resistance-for the attainment and regulation of a low speedwith varying torque. The variable impedance may be an electron tube or tubes, the impedance of which is controlled by means of a voltage impressed upon the control electrode of the tube. The invention will be more fully explained in connection with the accompanying drawings which illustrate an embodiment of the invention for the control of a threephase induction motor driving a printing press or the like, and which is required to operate at adjustable relatively high speeds at normal,

torques, must start with a relatively high torque and for threading the paper into the machine must be operable at a very low speed requiring a relatively high torque.

The present invention has for one of its objects to provide special means which afiord a wide range in speed and simultaneously a wide range in torque with a single motor.

Another object of the invention is to provide speed regulating means which are rapid in response to varying conditions in load.

Another object is to provide means a-ifording in an induction motor drive low stable speeds for rapidly varying loads on the motor.

Another object is to provide a single'motor drive affording high torques up to the maximum motor torque at very low constant speed.

Another object is to provide means for quick stoppage of an alternating current motor by dynamic braking.

Another object is to provide in a system. ofthe aforementioned type a regulating impedance which is continuously variable between substantially zero and infinity.

Another object is to provide means affording stable operation of a gaseous tube at relatively #low load currents, without affecting its ultimate load current carrying capacity.

The drawings in addition to Fig. 1, which has already been described, include the following:

Fig. 2, illustratinga motor control system employing grid-controlled gaseous tubes to control the motor primary current;

Fig. 3 which is a modification of the system of Fig. 2, employing igm'trons to carry the primary current;

Fig.4 which is a modification of the system of Fig. 2 and Fig. 3;

Figs. 5 and 6 which illustrate certain characteristicsof the modifications of Figs. 3 and 4, respectively, while Fig. "l which illustrates another modification of the systems shown in Figs. 2, 3 or 4.

Referring to Fig. 2, the same illustrates an induction motor [0, having a three-phase primary winding ll] and a three-phase secondary winding I The primary winding is connectable to the bus bars L L and L of a threephase source of supply through an electromagnetic switch I I, having an energizing winding I I, and normally open main contacts Il H, and li The contacts ll connect the bus bar L to one terminal of the Winding Ill. The contacts ll." connect the bus bar L to another terminal of winding Ill while the contacts ll are connected between the bus bar L and the cathode l2 of a gaseous electron tube l2. A gaseous tube 13 has an anode l3 which is connected to the cathode l2 and a cathode l3 which is connected to the anode 12 of the tube 12. The tubes l2. and I3 are also provided with control electrodes l2 and I3, respectively. Connected across the lines L I? is acenter tapped impedance H. The center tap 0f the impedance I4 is connected to one terminal of [the] a. primary winding I5 of a transformer IS. The other terminal of said primary winding I5? is connected to one of the endterminals of the impedance l4 through a resistor Land is also connected to the other end terminalof the impedance l4 through the winding fl iof a saturable reactor 11 which is also provided with a. saturating winding Il The transformer I5 is also provided with secondary windings I 53 and [5 The winding [5 is connected between the cathode l2 and the control electrode 12 while the winding 15 is connected between the cathode [3 and the control electrode 13.

The secondary winding tu of the motor In is connected to resistors 18, I9,.and 20, one termiwinding Zi Similarly, the intermediate taps between the resistors [8 I8 l9, I5 20, 20

are connected to the three poles of a triple contact "22 of an electromagnetic switch 22 having an energizing winding 22 and the common terminals of the resistors 18 and I8, l9 and 19, and 20 and 20 are each connected to one of the terminals of a triplecontact switch 23 of an electromagnetic .switch 23 which is also provided 'with an energizing winding "23 One'terminal of the windings 12i 22, and 23 is connected to the positive terminal of a direct current source. 24 Whilathe other terminals of said windings are connected to the anodes 25 26 and- 2! of electron tubes 25, 26, and 21, respectively. 'Iheseelectron tubes are also provided with cathodes 25 25 and 21, respectively, connected to the negative terminal of the voltage source 24 and with control electrodes 25, 26, and 21, respectively. A voltage dividing resistor 29 islconnected between the positive and negative terminals of a second direct current voltage source 28. The controlelectr-ode 21 is connected in series with a current limiting resistor 30 to an adjustable contact 29 of the voltage divider 29. The control electrode 26 is connected through a current "limitingresistor 3| to a movable contact 29 of the voltage divider 29, while the control electrode 25 isconnected through a current limiting resistor 32 to a third movable contact 23 of said voltage divider 29.

Arranged so as to rotate with the armature of the motor I0 is a tachometer generator 33, the output voltage of which is proportional .to the speed of the motor 10. The tachometer 33 may be of any suitable type yielding a unidirectional voltage. The diagram shows a tachometer generator which may be of the permanent magnet type or which may be provided with a separately excited'fi'eld winding (not shown).

The negative terminal of the generator 33 is connected through. a current "limiting resistor, to the control electrode 35 of an'electrontube 35 which is also provided with a cathode 35 and an anode'35 The'cathode'35 and anode 35 are. connected to'the negative and positive terminals respectively,-of adirect current voltage source 36, the connection of the anode being through a'resistor 31. The anode 35 is'also connected through a current limiting resistor to the control electrode 38 of an electron tube 38 which is also provided with an anode 38 connected through a resistor 39 to the positive terminal of the source 36 and with an anode'3ll which is connected to the movable contact of a voltage dividing resistor 40. The resistor I0 is connected across the terminals of the 'source36. The anode 38! is directly connectedto the control electrode 4I-of an electron-tube 4|, which is also providedwith a cathode 4| connected to theposltive terminal of the voltage source 36 and with, an anode M connected through a resistor 42 to one. terminal of the winding N of saturable re actor I]. The second terminal of the Winding l'l is connected to the positive pole "of a direct current voltage source 43. The negative termi-' the .equipmenttack-toits initial cane.

hit is desired a time; ass, that is, to. rotate it step by step, by momentarily supplying current to the motor, the inch button 46. is depressed. This completes the energizing circuit of the electromagnetic main switch ll fromline 'L xthroughswitch contacts 45 and 4.6 through the energizing winding H to line IF. and the motor,

primary winding- I is again connected to the line as ai'oredescribed. The-motor will turn over and ifit attains a sufficient speed the accelerating. switches 2 l 22, and 23 operate in the manner afore'described. However, for inching, it is.-usu-- ally desired that the speed which the motor at-.-

This is accomplished by interrupting the circuit from the positive terminal of the tachometer 33 through the normally open contacts 43 to'the sliding contact-44 and completing a circuit from the positive terminal of the tachometer 33 through. the contacts 49 to the adjustable contact 44 the relay 49 not being energized upon the depression of the inching button 45. Thus by adjusting the contact 44*, the conduction of the tube 35 may be adjusted for the maximum speed which the motor may attain upon depression of the inching button 46. This speed may be only a small percentage of the full load speed of the motor and may be insuflicient to cause .closure of any of the accelerating switches 21*,

22 and 23 If it is desired to operate the press at a low threading speed, the slow push button switch 48 is closed. This energizes the winding 50 by a circuit from line L through switches 45 and 48, the energizing winding to the line I]. The relay [50 50 responds to close a maintaining circuit through contact 50 which parallels the switch 48 so that the relay 5!] remains energized when the push button 48 is released. At the same time the contact 50 is closed thereby completing the energizing circuit for the main switch ll from line L over contacts 45 and 50', through the winding ll to line L The motor speed is controlled by controlling the moment of ignition of the tubes l2 and [3 in response to the voltage impressed upon the tube 35 by the voltage divider 44 and the tachometer 33 in the manner aforedescribed. As the relay 49 is deenergized, the grid 35 is now controlled by the setting of the contact 44 If the motor is to be stopped when running at threading speed, it is merely necessary to operate the push button switch 45, which opens the maintaining circuit of the relay 50 and this in turn deenergizes the electromagnetic switch II as will be apparent.

The system illustrated in Fig. 2 embodies gridcontrolled gaseousdischarge tubes l2 and I3 connected in series with the motor primary winding. Under certain conditions, especially for larger motors, it is desirable to use mercury pool tubes known as ignitrons. In that case the system may be substantially the same as aforedescribed, except that the ignitrons are interposed in the motor circuit and are in turn controlled by thyratron tubes which are actuated in the manner aforedescribed.

Fig. 3 shows substantially only that part of the system which differs from that shown in Fig. 2. In the case of Fig. 3, the thyratron tubes control the. i nitron circuit; oith en ttons nd late; t n-ar c n c e n series w t the mot rr iemary circuit. The thyratrons l2 and I3 respond to. the control voltage impressed upon them by the secondary windings I5 and I 59 of transfornp er 15,. in. .the same manner as in the case oithe system of F but theyin turn. co ol the.

ignition current of the ignitrons. [The cathodes. l2 and I3 of the thyratrons. l2 and I3, respec tively, are connected. through current limiting re sisters 60 and GI,- respectively, to the ignitron electrodes 62 and 63, respectively, of thecpre;

responding .ignitrons G2 and 63. The anode 63 of the ignitron 531s connected to thethyratrorr anode[s l2? and] .|3P[, respectively]. anode I52 of ignitron 62 is connected to thyratron anode 12 to the cathode 63' and to one terminal of winding Ill. The cathode I52 is connected to the anode 63 and also through the contact llto the line L It will be apparent that the current in'the ignitrons is initiated at the momentv when the corresponding thyratrons become con-i ducting and the functioning of the system isin all other respects the same as has been explained in connection with Fig. 2.

It is well known that ignitrons will not operate successfully below a certain minimum current: Fig. 5 shows for a given load the voltage drop. through an ignitron from zero conduction to conduction for practically the full time during.

which its anode potential is positive with respect to the cathode. It also shows the minimum cur.- rent (I min.) below 'which the. ignitron will not function successfully. From this it Will be seen that if the external impedance in series with the ignitron is very high so that the current through the tube would be less than the aforestated mini.- mum, the ignitron does not function successfullyv in response to the efiect of its ignitron electrode.

Such conditions may obtain when the load on a motor which is controlled by the ignitron is very low, so that it would be diflicult if not impossible to obtain a very low creeping speed at low motor torques with the arrangement shown in Fig. 3.

Fig. 4 shows substantially only that part of the system which differs from that shown in Fig. 3. This arrangement provides for passing through the ignitron, in addition to the motor current, a supplemental current which together with the motor current maintains a sufllciently high current through the ignitron to cause it to function properly. This means consists of a saturablereactor 64, the alternating current winding 64 of-- which is connected in parallel with the motor Winding between the cathode 63 of the ignitron 63 and the bus bar L of Fig. 3. The saturating winding 64 of said reactor is connected in series with a rectifier 65, across the main electrodes of the ignitron 63. To smooth out the half-wave rectified current passing through the tube 65, a

smoothing condenser 66 is connected across the terminals of the winding 64. It will be seen that the current which passes through the winding 64 is a direct function if the voltage drop across-the ignitron 63. Hence when the voltage drop of the ignitron is high, the current in said winding I34 is high, whereas when the voltage across the ignitron is low, the current in the winding 64* is low.

It is further known that the current in the winding (i4 varies with the current in the winding 64. The current in the winding 64 is added to the current flowing through the tube 63 to the corresponding terminal of the motor winding.

Thus the total current flowing through the tube The...

.isithearesultantzofzthemctorcurrent and the current flcwmgithrcugh the: reactor avinding 64 :Referring. to Fig..- 6; the-tube. current is indicated byza substantially. straight. line. The' minimum .eurrentat which the tubevvill operate. consistently is indicated by.the-letter.A. Without the current --through the :Winding 64* .this would also be the minimum .current to the motor, and the .range .throughwhich thetubecould regulate the motor would'befrom the point C .inrthe diagram toithe full load-or 10(l:per--cent loadcurr'ent. As the tube eurrent'decreases, the voltage impressed upon the reactance winding M tir-icreases as indicated-by Elg. r6,'.-so that: thezcurrent through the winding flh'atfirstalso increases-butdue to the increased :voltage drop-through the tube, the current. in the windingifi l tendsto idecrease. As aresult, a balance obtained at; a certain point between the saturating efiect ofthe winding, and'the effect of rthe-voltagedropthrough the tubetfi3 upon the windingefifl At that point :the reactor .current .againdecreases with decreasingtube current-as shown inaFigpzfi. :Nevertheless, for the minimum tubercurrent' value. A, the currentjthroughv thereacterhas still asubstantialvalueso that the low- -er currentfB is--,availableifor the motor winding. .Hence-rthe:reaotor extendsthe range of control of the motors-to :much lower value as indicated .by

dynamic-braking of the motor to obtain a quick stop. IImaddition: tothe apparatus shown in-F-ig.

-2,-.thersystem.is provided-with an electromagnetic switch -10, having an energizin winding 10*, normallyopen contacts all) and 16 and normally closed-contacts 10 The-contacts Ill are connectedbetween-the anode-l2 and cathode l3, while-the contacts Hl and-"l0 are connected in .parallel with-the contacts II and II, respectively. The stop push button switch-45 of Fig. '2 isgprovided -.withsadditional normall open contacts-45 which-are closed .upon depression of the push {buttonandruponopening of the normally closed. contacts 4 5 lure-modification shown inaF-ig. '7. operates in thefollowing manner: If it .is desired to stop the pressafter threading or running, the push buttonA5= is depressed, thereby disconnecting the motor from the-line in-the .manner aforedescribed. But-as long -as the push buttonsw-itch- 45 is'held down; the..con-tacts .4li are closed, thereby establishing a circuit from line L over contacts 45 through winding Tlllstoline L This energizes thelswi-tch l0, therebyiestablishinga-circuit from line-L through contacts tube- I53, through the motor primary-winding- Ille. through contact 10 to. line L .While the opening ofwthe contacts Ill cuts the tube l2 out of circuit. As long as the motor.-rotates,.-it therefore actsas an alternating currentgenerator, its energy being dissipated as heat generated by the-currents induced in its secondary iwinding, thereby bringin the motor quicklynto astop.

- .'.'It will .be apparentthatinstead or; providing the contaets- 4.5 parka-push ..button---45, a-separate pushtbuttonjmey.begprovided .forthe. brakingoperation. Itrwll1.alsobezar pflrentsthatthe switch .10 may beremp oyedin connection with the-mod ficationsotEigss-fi. andA.

.ItWiJIJbenbviousthat instead of a singlemotor, 1a pluralitytof..-motors,' whose primary terminalsaare .connectedimparallel, may be controlled jointly-win: the!manner-zaforedescribed. It-is fu ther eleparent that -.-a single tachometer with go. singlepet of .a plurality of .the aforedescribed associated regulating devices may be.--emplOy.e.d toflointlyzcontrol a; plurality of motors,- each.provicledtw-ithzan indiuidualimpedance device.

iInasomeg-eases itwmayi-bezdesirabletopass only rart-lofithezmo cr primary (tl111$nt;.'0f onemhase through the\tubesrlflrandwltofiliig z or'the tunes Bland-"8:3 of thecsystem: illustrated in :fer control bYuiSllQhrfitlbBS. .irnssuch;even riarsuitable mpedancemay bezconnected in parallelrwithrthe r p ive tubes. -With thisrarrangementwonly thelcom-ponent ofthe totalieurrent which-passes through .1 the (tubes ;-;is -subject .150 control thereby and the minimum current supplied-to-:the motor iszthercurrentrcondueted .byvthe impedance when the .tuhesghave; beenrendered; non-conducting by the -1nfi-uence vo-f the controlling effect thereon.

.-1.. A-zmethod-iof controlling,;-through-icentrolecf a single dine HQOHLHGCtlOII thereof, a-polyhhase translating device. having all terminals connected to the i-lines :of -,=-a-polyphase; supply circuit which comprises smelting saidsingleconnection-dependent upon -an-zelectronic discharge; produced thereimand regulating haltcyclesof suchvd-ischarge-qin respectof; ratio :Qf conduction :and nomconlillction-zdurting half scyeles individually, thereby-to afford refit-crept cunbalanced'r-conditions -:t he translating device-in: assteplessrmann r throu h a :range which :may. ..xtend ;:iro m substantially balanced spolyphase conditions 1130 single phase conditions.

:2. iinrazcontrohsystem fora translating devic inrcombination, a source: of polyphase-eurrentsa translating :dcvice shaving a rpolyphase winding including a :pluralitywof terminals forconnecting it s'to sadd ssource *-to receive current therefrom, spaceridischarge; means; having-sencontrol-e1ement and being i interposed ebetweensaid source and onevofi saidt-terminals;;and--means to impress upon said .C0l'lbI'O1.Elem8nt a poten-tial varying. in response -to: an -operatingcharacteristic of said 'deviceand "regulating the ratio of conductionand nonconduotion "30f said "discharge means during individual i-half cycles-to ith-ereby afford, through potential regulation :of a ..single terminal of the polyphase *vvinding, current control-through -.a range whichmay extend from substantially -ba1- anced polyphase :condition of "the translating- 'device to single phase condition thereof.

3. Incawprintingfipress-control-system ;or the like; in combination,--a-source of 'polyphase current; a unotor having a polyphase primary wind ing including as. plurality of terminals for connecting'it to said source,- space discharge means having a :control element and being interposed between-said'sourceand one-of said terminals, and meansto impress upon said control element a potential varying in responseto the speed of said motor-and regulating the ratio of conduction and nonconduction of said discharge means during, individual half cycles to thereby afiord,'through potential regulation of a single terminal of the motor primary winding, motor control through a range which may extend from substantially balanced polyphase condition of the motor to single phase condition thereof. 4. In a printing press control system or the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, 'a space discharge device having a control element for varying its impedance interposed between said source and one of said terminals, means for impressing upon said control element an alternating potential whose frequency is that of said polyphase current, means afiording a potential which varies with the speed of said motor, and means to superimpose a resultant of said varying potential upon said alternating potential to vary the impedance of said device in response to the speed of said motor to afford, through potential regulation of a single terminal of the motor primary winding, motor control through a range which may extend from substantially balanced polyphase condition of the motor to single phase condition thereof.

5. In a printing press control system and the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, and a secondary winding, a space discharge device having a control element for varying its impedance interposed between said source and one of said terminals, means for impressing upon said control element an alternating potential whose frequency is that of said polyphase current, means afiording a potential which varies with the speed of said motor, means to superimpose a resultant of said varying potential upon said alternating potential to vary the impedance of said device in response to the speed of said motor, a variable impedance connected to said secondary winding, and means to vary said impedance in response to said varying potential.

6. In a printing press control system and the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, a space discharge device having a control element for varying its impedance interposed between said source and one of said terminals, means for impressing upon said control element an alternating potential whose frequency is that of said polyphase cur-. rent, means affording a potential which varies with the speed of said motor, and means to superimpose a resultant of said varying potential upon said alternating potential for varying the phase angle between the latter and the voltage impressed upon said device by said source to vary the impedance of said device in response to the speed of said motor.

7. In a printing press control system and the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, a space discharge device having a control element for varying its impedance interposed between said source and one of said terminals, a phase shifting network connected to said source and to said control element to impress a potential upon the latter, means aflording a voltage which varies with the speed of said motor, and means to impress upon said phase shifting network a resultant of said varying voltage to vary the impedance of said device in response to the speed of said motor.

- 8. In a printing press control system and the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, a single pair of space discharge devices connected inversely parallel to each other between one phase of said source and one of said terminals, each of said devices having a control electrode for varying its impedance, and means to impress upon said control electrodes a potential varying in response to the speed of said motor to thereby control the current passing through said devices.

9. In a printing press control system and the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source and a secondary winding, a pair of space discharge devices connected inversely parallel to each other and interposed between said source and one of said terminals, each of said devices having a control electrode for varying its impedance, a variable impedance connected to said secondary winding, means to impress upon said control electrodes a potential varying in response to the speed of said motor to thereby control the current passing through said devices, and means to vary said impedance in response to said varying potential.

10. In a printing press control system and the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, two space discharge devices, each having a control electrode for varying its impedance, means to connect saidt'er minals to said source and to interpose one of said devices between said source and one of said terminals, commutating means connecting the other of said devices inversely parallel with said one device for operating said motor as a prime mover and operative to alternatively disconnect said other device from circuit and to connect two of said terminals to said source with said one device interposed between said one terminal and said source for supplying a rectified current to said winding for dynamic braking of said motor, and means to impress upon said control electrodes 9. potential varying in response to the speed of said motor to thereby control the current passing through said devices.

11. In a control system for a translating device, in combination, a source of alternating current, a translating device having a winding including a plurality of terminals for connecting it to said source to receive current therefrom, space discharge means interposed between said source and one of said terminals, a variable impedance device connected between said one and another one of said terminals, and means for varying the impedance of said impedance device in accordance with the voltage drop through said discharge means.

12. In a printing press control system and the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, space discharge means having a control element for varying the impedance thereof interposed between said source and one of said terminals, means to impress upon said control element a potential varying in response to the speed of said motor to thereby control the current passing through said space discharge means, a variable impedance device connected :betweemsaiiisone -.and ainother'= one otssaid terwttfiinfilssarid means for varying the impedaneemi -"S'I ;idi' impda"n6e device inaccordance "with" the vcltage drop through-said spaee dischargemeans.

Imamrintingpress*control-'system and the ter, means aifording a vcitage which varies with the speed of said motorwm'eans to impz essupon said phase shifting network a resuitant obsaid varying voltage to "vary the impedance of said discharge device "in response tothe-spedofi said motor, ':a -variable" impedanceflevice connected between said oneand-" another "oneof said tern-iinalsr aiid means for =varying the impedance of said impdance-devficdin 'accoi' daneem i th the voltage drop-"through said-space 'd-istzh'arge device. 14;aima;printing*press'c'ontrol 'systemarid'the like; in combination; a 'source of. poiyphasepmrentp'a: motowhav i-ng 'a polyphaseprimary-winding -including a plurality of-terminals "for connecting? it -'-to saidsource, a pair -61 spaee discharge 1 devices a connected inversiy parallel to each :other' and interposed"- between one of said terminals and: said source, each of said'fiis'charge devices having a control electrodegmea-ns afioiding a: potential which varies with "the 1 'speedof said rmotor, manual slow speed-and high speed means i-or connecting said"'-te1-mina1s to said source and interposing said spac'edischarge devieesfibetween SEld'wSOUi-DE-fifid one ofsaid "tenmin'a'l's, :said manuiil *m'eans inchiding means affording different '='ratios between "said "varying potentialwand the =motor* 'speedtcr-*initiating uperati-on' otsaid=':motor iatfirela tivelv high- =running "speeds and :.;;at im-relatively w threading speed selectively, ian'd means to impress :said varying potential zupone said-"contnm electrodes to z thereby control, the-current passing throueh said devices. 15. in imprinting press contro1- system and "the like, sin combination: azsource "of. poiyphase current, a: motor. having a' polypha'se primary windinggzinclu ding a :plurality :01 terminals for connesting-it. toz'said :source, sa ffirs'tspace discharge device; a second: space-discharge device, each of said devices-having a; :contno1-:teiectrod'e' for varying: sits: impedancanmeans :to impress "(upon "said control: electrodes aspotentiai varying "in response to theispeed oft-said motonta'therebycontrol-the current passing through said devices, manual startingmieans operative-to connect said winding through said terminals to said source and to interpose said first: space discharge "device between said sourceandone of vsaid terminals .forxstarting and running, and? including means "tor-connect said secondspace discharge,devicevinversely parallel to said first space discharge device, and manualtstopping means operative to disconnect said second space discharge "device from circuit and render said starting-means ineffective to therebyafiord dynamic braking.

16. In a control I system, --combination, a source of polyphase current, .a motor having .a poly/phase primary windingincluding a, plurality of "terminals 'for connecting "it to said source, space discharge means having a control element and being interposed between said source and one of said terminals, and means to impress up- :zonf-saidscontrol-setement a potential varying imme- :sponse torthespeed op -said-moton andregzdating the: ratio: of: 2can-auctionand noneconductioaaaf said discharge means during individual new vcyc-les-. -to L-therebyswatord, through potential reg- ;ul'ationa-of a single terminal oft-the motor-pnimary iwinding, :motor control through arange which 2may extend a from substantially r-ba'lanced poly- :phase condition: ofthe motorxto-zsingle phase:con-- ditio n' th ere of.

1 7 J-Ima control system,'in combination, a source ofiphlyzihasecurrent; a motor havingcapolyphase primary winding includingaflplurality .ojzterminals for connecting it. to-zsaid source, -a.:sp-ace discharge device having a: control elementi jor .varyingz its impedance interposed between said source :and onef cf said I terminals, -means ifor impressing .upon said control element anialtennating potential .whose .trequency is that (it-said polyphasemcurrent, .means afiording a potential whichrvariesuwith" the rspeed" of said" motor, :and means" to superimpose a resultant 0fsaidflvarying potential iupon' said alternatingpotential to'aaary the impedance of said device in response ta the speed iof-said motor -toafford, through potential regulationof asingle terminal. of the motor primary winding, motor control f through a range which mayattend 'from' substantially-"balanced polyphase'condition of the motor. to -single phase condition" thereof.

'18. In a controll -system, in -combination; --a source of polyphase current, a motor' 'havingxa polyphase'primary winding including -a plurality of terminals for connecting it' tosaidsource;and a secondary winding, aspace discharge device having a control element for varying' its'impedance interposed between said sourceand-one of said terminals, means for impressing upon said control element an dlterna'ti-ng potential *whose frequency is "that 'of said 'po'lyphase =current, means afiording a potent'idl-whieh-varies with the speed 0)- said-"motor; means to'superimpose-n resultant ofsaidvarying potential-upon said a l ternatingpotential to vary the impedanceof said device in response to the-speed of said motorja variable *tmpdahceconnected to saidsecondary winding; 'andmeans to varysaid'impedance inresponse-to said varying potential.

1-9. In a-controlsy'stem; in-combinatioma source of pdlyphasecurrent; a'motor having a-polyphase primarywindin'g including a'pluralityoj terminals for connecting it to said source, a space discharge device "having a control'element for varying'its impedance-'--interposed'-between said source and oneof said terminals, means for impressing upon said control *element "an alternating "potential whosefrequency is that of said'polyphase current, me'ans' afiording a' potential which-varies with-"the speed 'ofsaid-motor, and means to superimposed] resultantofsaid-varying potential upon said'alternating potential for varying the phase angle between the latter and the 'voltageimpressed' upon'said'device by'said'source to vary the imped: ance-of-saiddevice in response to thespee'd of-said motor.

20. In a control system; in combination, a source 0'), polyphasecurrent, a motor having a polyphase primary winding including" a' plurality of "terminals'for'connecting it to-said'source, a spacedischarge device having a control element for varying its impedance interposed-betweensaid'source and one of-saidderntinals, 'a phase shifting network connectedto'saidsource and to said control element to impress a potential upon the latter, means afiording a voltage which varies with the as speed of said motor, and means to impress upon said phase shifting network 'a resultant of said varying voltage to vary the impedance of said device in response to the speed of saidmotor.

21. In a control system, in combination, a

source-of polyphase current, a motor having a polyphase primary windingincluding a plurality oI-terminals for connecting it to said source, a singlepair of space discharge devices connected inversely parallel to each other between one phasesofzsaidzpsource and one of said terminals, each of said devices having a control electrode for varying its impedance, and means to impress upon said control electrodes a potential varying in response to the speed of said motor to thereby controlrthe current passing through said devices.

'22. In a control system, in combination, a sourceof polyphase current, a motor having a polyphasemrimary winding including a plurality-ofifterminals for connecting it to said source, space discharge means having a control element for varying the impedance thereof interposed between'saidzsource and one of said terminals,

means togimpress upon said control element a potential varying in response to the speed of said motor to thereby control the current passing through said space discharge means, a variable impedance device connected between said one and another one of said terminals, and means for varying the impedance of said impedance device in accordance with the voltage drop through said space discharge means.

'23. In a control system, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, a space discharge device having a control element for varying its impedance interposed between said source and one of said terminals, a phase shifting network connected to said source and to said control element to impress a control potential upon the latter, means afiording a voltage which varies with the speed of said motor, means to impress upon said phase shijting network a resultantofsaid varying voltage to vary the impedance of said discharge device in response to the speed of said motor, a variable impedance device connected between said one and another one of said terminals, and means for varying the impedance of said impedance device in accordance with the voltage drop through said space discharge device.

' 24. In a control system, in combination, a source of polyphase current, a motor having a polyphase primary winding includin a. plurality of terminals for connectingit to said source, a pair of space discharge devices connected inversely parallel to each other and interposed between one of said terminals and said source, each of said discharge devices having a control electrode, means affording a potential which varies with the speed of said motor, manual slow speed and high speed means for connecting said terminals to said source and interposing said space discharge devices between said source and one of said terminals, said manual means including means afl'ording dijferent ratios between said varying potential and the motor speed for initiating operation of said motor at relatively high running speeds and at a relatively low threading speed selectively, and means to impress said varying potential upon said control electrodes to thereby control the current passing through said devices.

all)

- 25. A-motor control. system, comprising a. mat-- ti-phase alternating-current motor, multi-phase circuit means connected to said motor for supplying alternating-current 'energization, a controllable discharge tube plate connectedwitha lesser number of phases of said circuit means for un"- balancing the multi-phase energization' depending upon the effective impedance of the tube, said tube having a control circuit for'varying said impedance, condition responsive control means connected to said motor for providing a control voltage varying in accordance with the motor speed, and circuit means disposed between said control means and said control circuit for causing the latter to vary said impedance in response to variationsof said control voltage.

26. A motor control system, comprising an altemnating-current multi-phase motor having primary terminals, multi-phase circuit means connected to said-terminals-for supplying alternating current, only one phase of said circuit means having two controllable discharge tubes parallel connected to each otherin back-to-baclc relation and series-connected in said one phase of said circuit means, each of said tubes having a control circuit for varying the conductive inter= vals ofthe tube relative to the voltage cycles of said current, speed-responsive control means connected with said motor for providing a control voltage varying in accordance with the motor speed and connected 'to said grid circuits for varying said intervals in dependence upon said control voltage.

27. A motor control system, comprising an alternating-current multi-phase motor having primary terminals, multi-phase circuit means connected to said terminals for supplying alternating current, only one phase of said circuit means having a controllable discharge tube series-connected with said circuit means, said tube having a control circuit for varying the conductive intervals of the tube, a source of variable control voltage connected to said motor so as to provide-a control voltage varying in dependence upon the motor speed, a source of a constant control volt= age, said two voltage sources being connected to each other and being both connected -to said control circuit for controlling the latter in accordance with the resultant efiect of the two control voltages, and operator-actuable control means associated with one of said sources for selectively adjusting the variable control voltage and constant control voltage relative to each other so as to obtain a given control condition of said control circuit at a motor speed determined by the selected setting of said control means.

WILLIAM H. ELLIOT.

REFERENCES CITED The following references are of record in the file of this patent or the original patent:

UNITED STATES PATENTS 

